Wheel loader machines known in the art are used for moving material from one place to another at a worksite. These machines include a body portion housing the engine and having rear wheels driven by the engine and an elevated cab for the operator. A front non-engine end frame with the front wheels is attached to the body portion by an articulated connection allowing the end frame to pivot from side-to-side when the front wheels are turned to steer the machine. The end frame further includes linkages, such as Z-bar linkages, for manipulating an implement of the machine. A pair of lift arms coupled to the end frame are raised and lowered by corresponding lift cylinders to adjust the elevation of the implement above the ground. Where Z-bar linkages are used, the tilt of the implement (rotation of the implement about a pivot connection at the end of the lift arms) is controlled by a tilt lever and tilt link coupled between the lift arms and the implement, and driven by a tilt cylinder. An example of a wheel loader machine implementing a Z-bar linkage is provided in U.S. Publication No. 2006/0291987, published Dec. 28, 2006.
The wheel loader machines may be able to move many different types of materials depending on the requirements of the job site. Consequently, the machines are designed to manipulate different types of implements. A bucket may be the appropriate implement for moving what are considered to be loose materials, such as earth, clay, sand and gravel. When moving the loose materials from a pile to a truck, for example, the lift arms and tilt links are manipulated to place the cutting edge of the bucket parallel to the ground and near the bottom of the pile. After the bucket digs into the pile, the tilt links rack the bucket back to gather a maximum load in the bucket, and the bucket is raised out of the pile by the lift arms for transport of the material to the truck. Once there, the tilt links unrack the bucket and tilt the bucket forward to dump the load into the truck.
Pallet forks may be an appropriate implement for other types of materials, such as palletized cargo. Forks may also be appropriate for lifting cylindrical payloads like sewer pipe, telephone poles and tree trunks. For these types of payloads, full racking of the implement may rarely be necessary, and in some applications undesirable, but maintaining the forks parallel to the ground or tilted slightly upward as the lift arms are raised and lowered may be advantageous to prevent the load from sliding off the front of the forks. This may occur when the tilt angle of the forks becomes too shallow and the wheel loader machine stops suddenly. Other types of implements are also used on wheel loader machines, and may similarly have divergent movement requirements for moving the material for which they are designed.
In many implementations, the wheel loader machines are configured so that a variety of implements may be used interchangeably on a single machine. In some implementations, a universal coupler may be connected to the lift arms and tilt linkages. The implements may have corresponding connectors that mate with the coupler to attach the implement for use. As discussed above, each implement will have differing ranges of motion when moving the materials for which they are designed. In some situations, these motions may be complimentary, whereas in other situations the motions may cause conflicting requirements for the configurations of the lift arms and tilt linkages. In the designing of the wheel loader machine, the requirements of one particular implement drive the design of the lift arms and the Z-bar linkages to meet the needs of the target customers. The performance of other implements may be met by coincidence, but are typically compromised in favor of the dominant design implement. Therefore, a need exists for an improved wheel loader machine design implementing a Z-bar linkage that provides the desired performance for two or more implements, such as buckets and forks, by choice instead of happenstance.